The alignment of a vehicle's wheel plane relative to the path traveled by the vehicle affects not only the handling of the vehicle but also affects the wear on the tires. As used here, alignment refers to camber, toe, and thrust. Camber is the angle between the vertical axis of the wheel and the vertical axis of the vehicle. Positive camber refers to an angle where the top of the wheel is farther away from the center of vehicle than the bottom of the wheel. Negative camber refers to an angle where the bottom of the wheel is farther away from center of the vehicle than the top. Generally speaking, camber changes of even slightly more than a fourth of one degree can impact tire wear. Toe is the angle each wheel makes with the longitudinal axis of the vehicle. Positive toe, also referred to as toe in, is a condition where the front of the wheel is pointing in or towards the center line of the vehicle. Negative toe, also referred to as toe out, is a condition where the front of the wheel points out or away from the center line of the vehicle. Thrust is the resulting direction of travel of an axle as opposed to the direction that might be expected from the orientation of the tires on the axle. Generally speaking, toe changes of even one-tenth of a degree can have an impact on tire wear.
The contribution of tire alignment to tire wear can be particularly problematic with vehicles used for transporting heavy loads. As different weights are loaded and unloaded from the vehicle (used herein to refer to both motorized vehicles as well as trailers), one or more of the vehicle's axles will likely flex. Depending upon the amount of weight and the rigidity of the axle, the axle may bow and cause the wheels to orient towards negative camber—a condition that can cause unfavorable tire wear. Once the weight is removed, the axle may recover and again affect the alignment of the wheels. Because of factors such as the additional costs and amount of material that would be required, increasing the stiffness of the axle to resolve camber issues may not be practical.
A proposed solution for addressing tire alignment problem is to incorporate a coupling into the axle and include a special shim between the coupling interface. More specifically, a tapered shim can be configured into the axle assembly to allow for the altering or correction of the relative alignment of an axle or spindle and, therefore, the alignment of the wheel and tire that are carried on the axle or spindle. Unfortunately, currently available shim assemblies generally have certain disadvantages. Typically, disassembly of the axle into various components is required such as e.g., removal of the wheel, spindle, or both before the shim can be adjusted. For trailer loads that may vary substantially, a labor intensive process to access and adjust the shim may not be practical. Additionally, axles are frequently hollow and contain fluids such as lubricants or air for pneumatic brakes. Shim systems that do not allow for a means of sealing such fluids can be unacceptable in certain applications.
Therefore, a need exists for improved methods and apparatus for adjusting or correcting axle alignment. A system that allows for adjustment while minimizing the amount of disassembly and labor required would be particularly advantageous. Additional usefulness would be provided by a system that allows for adjustment of the alignment of an axle used to contain a fluid.